#include <stdio.h>
#include <stdlib.h>
#include <poppler.h>
#include <cairo.h>

#define IMAGE_DPI 150

int main(int argc, char *argv[])
{
  PopplerDocument *document;
  PopplerPage *page;
  double width, height;
  GError *error;
  const char *pdf_file;
  const char *png_file;
  gchar *absolute, *uri;
  int page_num, num_pages;
  cairo_surface_t *surface;
  cairo_t *cr;
  cairo_status_t status;

  if (argc != 4) {
    printf ("Usage: pdftoimage input file.pdf output file.png page\n");
    return 0;
  }

  pdf_file = argv[1];
  png_file = argv[2];
  page_num = atoi(argv[3]);
  g_type_init ();
  error = NULL;

  if (g_path_is_absolute(pdf_file)) {
    absolute = g_strdup(pdf_file);
  } else {
    gchar *dir = g_get_current_dir();
    absolute = g_build_filename (dir, pdf_file, (gchar *) 0);
    free (dir);
  }

  uri = g_filename_to_uri (absolute, NULL, &error);
  free (absolute);
  if (uri == NULL) {
    printf("%s\n", error->message);
    return 1;
  }

  document = poppler_document_new_from_file(uri,NULL, &error);
  if (document == NULL) {
    printf("%s\n", error->message);
    return 1;
  }

  num_pages = poppler_document_get_n_pages(document);
  if (page_num < 1 || page_num > num_pages) {
    printf ("page must be between 1 and %d\n", num_pages);
    return 1;
  }

  page = poppler_document_get_page (document, page_num - 1);
  if (page == NULL) {
    printf("poppler fail: page not found\n");
    return 1;
  }

  poppler_page_get_size(page, &width, &height);

  /* For correct rendering of PDF, the PDF is first rendered to a
     transparent image (all alpha = 0). */
  surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,
				       IMAGE_DPI * width / 72.0,
				       IMAGE_DPI * height / 72.0);
  cr = cairo_create(surface);
  cairo_scale(cr, IMAGE_DPI/72.0, IMAGE_DPI/72.0);
  cairo_save(cr);
  poppler_page_render(page, cr);
  cairo_restore(cr);
  g_object_unref(page);

  /* Then the image is painted on top of a white "page". Instead of
     creating a second image, painting it white, then painting the PDF
     image over it we can use the CAIRO_OPERATOR_DEST_OVER operator to
     achieve the same effect with the one image. */
  cairo_set_operator(cr, CAIRO_OPERATOR_DEST_OVER);
  cairo_set_source_rgb (cr, 1, 1, 1);
  cairo_paint(cr);

  status = cairo_status(cr);
  if (status)
    printf("%s\n", cairo_status_to_string(status));

  cairo_destroy(cr);
  status = cairo_surface_write_to_png (surface, png_file);
  if (status)
    printf("%s\n", cairo_status_to_string(status));

  cairo_surface_destroy (surface);

  g_object_unref(document);

  return 0;
}
